For the coarsest level, an empty DisjointBoxLayout is passed in for coaserDisjointBoxLayout. Inside the routine, we cast away const-ness on the data members for the assignment. The arguments passed in are maintained const. (coding standards). a_nRefine is the refinement ratio between this level and the next coarser level. a_numGhosts is the number of ghost cells in each direction.

For the coarsest level, UcoarseOld and UCoarseNew are empty LevelData<EBCellFAB> objects. Also, either UCoarseOld or UCoarseNew might be empty to indicate that t(nf) = t(nc) the one grid is at the current time and interpolation is not required for boundary condition generation. U must be defined on the same DisjointBoxLayouts as were used in define(...) Coarse flux register is flux register with the coarse level. Fine flux register is the flux register with the fine level. To the finer level FR, this level is the coarse level. To the coarser level FR, this level is the fine level.